The planned research examines a process hypothesized to affect aggression that harms multiple persons (i.e., mass violence). Naturalistic studies and controlled experiments identify social rejection as an antecedent of aggression. Rejection, however, cannot account exclusively for aggression that harms multiple persons - particularly when the multiple victims did not directly reject the perpetrator. It is proposed that rejection functions synergistically with perceived groupness to affect mass violence. Individuals rejected by a member of a salient group might associate rejection with the group and, subsequently, retaliate against all group members. Two experiments and a questionnaire provide preliminary evidence for the synergistic effect. The experiments manipulated rejection and perceived groupness and demonstrated that those factors interacted such that participants behaved most aggressively against an aggregate of persons when a member of the [unreadable] aggregate rejected the participant and the aggregate appeared to be an entity-like group. The questionnaire study replicated those results by demonstrating that the frequency with which high school students fantasize about harming social groups varies as an interactive function of their rejection experience with the groups and the extent to which they perceive the groups to be entity-like. Two proposed studies expand the preliminary evidence and explore moderators and mediators of the synergistic effect. Study 1 examines if individual differences associated with perceived groupness influence the tendency for rejected persons to generalize aggression against all members of a social aggregate. Study 2 tests if cognitive/affective associations formed between the rejection experience and the salient group mediate the synergistic effect of rejection and groupness on mass violence. [unreadable] [unreadable]